The Japanese won by a landslide, 60 votes to Istanbul's 36. Abe, who left early from a Group of 20 summit in Russia to make his pitch at the meeting in Buenos Aires, promised the International Olympic Committee that concerns about the leaking Fukushima nuclear plant 230 km (140 miles) from Tokyo were unfounded.

Fixing the IOC members with a level gaze, he said: "It has never done and will never do any damage to Tokyo. There are no health-related problems until now, and nor will there be in the future -- I make the statement to you in the most emphatic and unequivocal way."

The plant's operator has said hundreds of tonnes of radioactive water are pouring into the Pacific Ocean each day, and radiation levels have spiked.

Abe's government said this week it will spend almost half a billion dollars to try to fix the water crisis and on Saturday he told the IOC: "Let me assure you the situation is under control."

MASTERFUL ORATORY

Tokyo won the right to stage the sporting extravaganza for the second time, having hosted in 1964 when the Games first went to Asia.

It was an enormous prize after two years of intense lobbying and tens of millions of dollars spent, and Abe was thrilled.

"I would like to thank everyone in the Olympic movement and we will host wonderful Olympic Games," a beaming Abe told Reuters just seconds after the result.

Bid leader Tsunekazu Takeda was in tears as he said: "It is a great honour that Tokyo has been chosen.

"The first thing I will do when I return is to thank all of Japan," he told Reuters after hugging dozens of IOC colleagues.

For Istanbul it was a fifth unsuccessful bid in the last six votes to host a summer Olympics.

They had pitched their bid on the appeal of a new region for the Games and as a vehicle to help peace in the Middle East, but the conflict in neighbouring Syria came and recent anti-government demonstrations in Turkey overshadowed the bid.

The Istanbul bid's sports director Alp Berker was searching for a reason for rejection as he told Reuters: "I don't know... there are too many variables, maybe it's the timing, maybe it's something else."

When asked if the Syrian crisis had damaged their chances, he said: "We tried to tell them it was not the case, because it's a global issue. Really I don't know what the members are thinking when they're pushing the button."

IOC vice-president and presidential candidate Thomas Bach described the decision as new versus old.

"I think it is an election between a traditional candidature and new grounds, and today it was the traditional candidature that won," he told Reuters.

BOOST FOR ABE

Madrid, which had pitched a safe, affordable, "sensible" bid had been earlier eliminated first in a secret vote by IOC members on a head to head with Istanbul after the two cities were tied in second place after the initial vote. Madrid's attempt to host 2020 had been a third consecutive bid.

Tokyo is planning to incorporate existing venues and has estimated a non-Games budget of around $4.4 billion compared to $3.4 billion for the actual event.

It already has a war-chest of some $4.5 billion in the bank.

The victory is expected to boost Abe's popularity, and could potentially spur his signature pro-growth policies for the world's third-biggest economy.

A successful Tokyo bid should boost confidence -- a key ingredient of Abe's economic success so far -- and bring real gains in terms of construction and tourism to the nation.

The next summer Olympics will be hosted by Rio de Janeiro in 2016. The preparations for that Games have been plagued by delays and complications, and a decision for Tokyo 2020 is a return to safer waters for the Olympic movement. (Additional reporting by Alexandra Ulmer, Karolos Grohmann and Rex Gowar; Editing by Mitch Phillips and Peter Henderson)